This invention relates to a variable displacement pump used as a hydraulic source and so on of a power steering apparatus of a vehicle.
U.S. Pat. No. 6,524,076 B2 (corresponding to Japanese Patent Application Publication No. 2001-304139) shows a variable displacement pump for a power steering apparatus of a vehicle. This variable displacement pump includes an adapter ring disposed in a pump body; a cam ring disposed radially inside the adapter ring, and arranged to swing about a support shaft disposed in an axial direction at a lower portion of an inner circumference surface of the adapter ring; a drive shaft rotatably supported through forward and rearward bearing bushes in the pump body; and a rotor connected with the drive shaft by a serration portion located at a substantially central portion of the drive shaft in the axial direction, and arranged to rotate within the cam ring.
In an outer circumference portion of the rotor, there are provided a plurality of vanes each moved in the radial direction from one of a plurality of slots formed in the radial directions. Moreover, there is provided a pressure plate sandwiching the cam ring and the rotor with the rear body in the axial direction. The pressure plate is formed with an inlet port opened in a region in which the volumes of the pump chambers are increased, and an outlet port opened in a region in which the volumes of the pump chambers are decreased.
Moreover, there are formed a first fluid pressure chamber and a second fluid pressure chamber radially outside the cam ring, on the both sides of the cam ring. There is provided a pressure regulating valve arranged to regulate the pressure introduced into the first fluid pressure chamber or the second fluid pressure chamber. Within the pressure regulating valve, there is provided a relief valve arranged to relieve to the pump induction side when the fluid pressure of the pump discharge pressure is equal to or greater than a predetermined value.
Moreover, in the discharge passage connected with the outlet port, there is provided a metering orifice arranged to regulate the discharge flow rate to the power steering apparatus. Furthermore, in a branch passage bifurcated from the downstream side of the metering orifice, and connected with the relief valve, there is provided a pilot orifice. This pilot orifice is arranged to regulate the flow rate which the relief valve relieves when the pump discharge quantity is increased.
Although this patent document of the earlier technology does not disclose, in a passage connecting the outlet port and the high pressure chamber of the pressure regulating valve, there is provided a damper orifice arranged to decrease the pressure pulsation of the fluid pressure introduced into the high pressure chamber.
The pressure difference between the forward side and the rearward side of the metering orifice is introduced into the first and second fluid pressure chambers. Consequently, the cam ring is swung in one direction, and the volumes of the pump chambers are varied to regulate the pump discharge quantity.